156 



ADDENDA, ETC. 



Fig. 260. 



Ancylus "borealis, Mouse. — Shell elliptical, solid, light yellow, 

 apex elevated, rounded, very obtuse, nearer the 

 posterior margin of the shell ; lateral slopes steep, 

 anterior slope slightly convex, near the apex ; 

 posterior slope straight. Fine regularly interrupted 

 radiating lines mark the surface of the shell from 

 the apex to the borders ; incremental lines irregu- 

 lar. Length .14 inch, breadth .09 inch, height .06 

 inch. 



This species resembles A. tm-dus in its general 

 form. It is much smaller, however, and has a 

 Ancylus horealis. ^^rong heavy shell. 



Discovered by John M. Gould, at Patten, in the 

 northern part of the State. {Morse.) 



Ancylus horealis, Mokse, Jouru. Portland Soc. I, 45, f. 103, 104. 



Acroloxus OValas, Moese. — I propose this and the following species 



Tith some reluctance, as the specific characters of nearly all the species 



of this genus are but faintly marked, and the danger of multiplying false 



species is but too apparent ; still, believing these to be 



new, I present them. 



Shell very small, depressed, irregularly ovate, apex 

 nearly central, round, smooth, and blunt, slightly in- 

 clined to the left, slopes irregular, caused by different 

 periods of repose and growth, posterior slope in most 

 specimens straight, anterior slope convex, lateral slopes 

 steep, shell widening anteriorly ; lines of accretion 

 extremely fine, visible within but requiring a magnifier 

 to discern them without, being greatly obscured by fine 

 grains of sand agglutinated to the surface. Periostraca 

 pale yellow, the surface when magnified exhibits about fifty-five delicate 

 ribs, which radiate from the apex to the periphery of the shell. Length 

 .12 inch, breadth .10 inch, height .06 inch. 



This species was discovered by John M. Gould, in the Androscoggin 

 River, at Bethel, Maine, in 18.54. I have since found it in the above 

 locality clinging to the under side of stones near the shore, in positions 

 where it could in no way reach the surface of the water. (Morse.) 



Ancylus ovalis, Morse, Journ. Portland Soc. I, 44, f. 101, 102. 



The descriptions and figures of this and the preceding speeies 

 are copied from Morse. 



Ancylus ooalis. 



On p. 103, before Planorbis, the following should be inserted : — 



SruKAMiLY PLANORBINyE. 

 Sliell spiral, discoidal or depressed, many whirled ; aperture crescentic. 



